1. Field of the Invention
The present invention relates to an optical drive device for performing information recording or reproduction of recorded information by formation of a mark by focusing a first light at a necessary position in a recording layer of an optical recording medium by an objective lens and, more particularly, to an optical drive device for focusing a second light on a reflection film, in which a position guide element of the optical recording medium is formed, through the objective lens and enabling a spot position of the second light to follow the position guide element based on the reflected light of the second light focused on the reflection film so as to control the position of the objective lens, and a tilt detection method of such an optical drive device.
2. Description of the Related Art
As an optical recording medium for recording/reproducing a signal by irradiating a light, for example, a so-called optical disc such as a Compact Disc (CD), Digital Versatile Disc (DVD) or Blu-ray Disc (BD) (registered trademark) have come into wide use.
With respect to an optical recording medium which is a next-generation optical recording medium widely used in the present state of the CD, the DVD, the BD and the like, first, the present applicant proposes a so-called bulk recording type optical recording medium described in Japanese Unexamined Patent Application Publication No. 2008-135144 or 2008-176902.
Here, bulk recording indicates, for example, a technology of realizing a large amount of recording capacity by irradiating a laser beam to an optical recording medium (bulk type recording medium 100) having at least a cover layer 101 and a bulk layer (recording layer) 102 by sequentially changing a focusing position so as to perform multi-layer recording in the bulk layer 102, as shown in FIG. 20.
In such bulk recording, Japanese Unexamined Patent Application Publication No. 2008-135144 discloses a recording technology which is called a so-called micro hologram method.
The micro hologram method is divided into a positive type micro hologram method and a negative type micro hologram method, as shown in FIGS. 21A and 21B.
In the micro hologram method, a so-called hologram recording material is used as a recording medium of the bulk layer 102. As the hologram recording medium, for example, a photopolymerizable photopolymer or the like is widely known.
As shown in FIG. 21A, the positive type micro hologram method is a method of focusing two opposing light fluxes (light flux A and light flux B) at the same position so as to form a minute interference fringe (hologram) and using the minute interference fringe as a recording mark.
The negative type micro hologram method shown in FIG. 21B is a method of erasing an interference fringe formed in advance by laser beam irradiation and using the erased portion as a recording mark, in opposition to the positive type micro hologram method.
FIGS. 22A and 22B are diagrams illustrating the negative type micro hologram method.
In the negative type micro hologram method, before performing a recording operation, as shown in FIG. 22A, an initialization process for forming an interference fringe in the bulk layer 102 is performed in advance. In detail, as shown in the drawing, light fluxes C and D by parallel lights are oppositely irradiated so as to form such an interference fringe in the overall bulk layer 102.
After the interference fringe is formed in advance by the initialization process, as shown in FIG. 22B, information recording is performed by forming an erasing mark. In detail, by irradiating a laser beam according to recording information in a state of focusing on an arbitrary layer position, information recording by the erasing mark is performed.
The present applicant proposes, for example, a recording method of forming a void (hole) disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902 as a recording mark, as a bulk recording method different from the micro hologram method.
The void recording method is, for example, a method of irradiating a laser light beam to the bulk layer 102 formed of a recording material such as a photopolymerizable photopolymer with relatively high power so as to record a hole (void) in the bulk layer 102. As described in Japanese Unexamined Patent Application Publication No. 2008-176902, the formed hole portion has a refractive index different from that of the other portion of the bulk layer 102 and thus the light reflection ratio of the boundary portion thereof is increased. Accordingly, the hole portion functions as a recording mark and thus information recording by formation of a hole mark is realized.
In such a void recording method, since the hologram is not formed, recording is completed by light irradiation from one side. That is, as in the positive type micro hologram method, it is not necessary to focus two light fluxes at the same position so as to form the recording mark.
In addition, in the comparison with the negative type micro hologram method, there is a merit that the initialization process is not performed.
Although, in Japanese Unexamined Patent Application Publication No. 2008-176902, an example of irradiating a pre-cure light before recording at the time of performing void recording is described, void recording is possible even when the irradiation of the pre-cure light is omitted.
However, even in the bulk recording type (simply also called bulk type) optical recording medium in which the above various recording methods are proposed, the recording layer (bulk layer) of the bulk type optical recording medium does not have an explicit multilayer structure in the sense that, for example, a plurality of reflection films is formed. That is, in the bulk layer 102, a reflection film and a guide groove of every recording layer included in a general multilayer disc are not provided.
Accordingly, in the structure of the bulk type recording medium 100 shown in FIG. 20, focus servo or tracking servo is not performed during recording in which the mark is not formed.
Accordingly, practically, in the bulk type recording medium 100, a reflection surface (reference surface) which becomes a reference having guide grooves shown in FIG. 23 is provided.
In detail, the guide grooves such as pits or grooves are formed in a lower surface side of the cover layer 101 and a selective reflection film 103 is formed thereon. The bulk layer 102 is laminated on the lower layer side of the cover layer 101, on which the selective reflection film 103 is formed, with an adhesive material interposed therebetween as an intermediate layer 104 of the drawing, such as a UV curing resin.
After such a medium structure is formed, as shown in FIG. 24, a second laser beam is irradiated to the bulk type recording medium 100 as a position control laser beam, separately from a laser beam (first laser beam) for recording (or reproducing) a mark.
As shown, the first laser beam and the second laser beam are irradiated to the bulk type recording medium 100 through a common objective lens.
At this time, if the second laser beam reaches the bulk layer 102, the mark recording in the bulk layer 102 may be adversely affected. Accordingly, in the bulk recording method of the related art, the laser beam having a wavelength range different from that of the first laser beam is used as the second laser beam, and the selective reflection film 103 having wavelength selectivity, which reflects the second laser beam and transmits the first laser beam is provided as the reflection film formed on the guide groove forming surface (reference surface).
On the above assumption, the operation at the time of mark recording will be described with reference to FIG. 24.
First, when multilayer recording is performed with respect to the bulk layer 102 in which the guide grooves or the reflection film is not formed, the layer position for recording the mark in a depth direction in the bulk layer 102 is set in advance. In the drawing, the case where a total of 5 information recording layers (mark forming layers) L including a first information recording layer L1 to a fifth information recording layer L5 is set as a layer position (mark forming layer; also called an information recording layer) for forming the mark in the bulk layer 102 is shown. As shown, the layer position of the first information recording layer L1 is set to a position separated by a first offset of-L1 in a focus direction (depth direction) from the selective reflection film 103 (reference surface) in which the guide grooves are formed. The layer position of the second information recording layer L2, the layer position of the third information recording layer L3, the layer position of the fourth information recording layer L4 and the layer position of the fifth information recording layer L5 are set to positions separated from the selective reflection film 103 by a second offset of-L2, a third offset of-L3, a fourth offset of-L4 and a fifth offset of-L5, respectively.
During recording in which the mark is not yet formed, focus servo and tracking servo are not performed based on the layer positions in the bulk layer 102 with respect to the reflected light of the first laser beam as a target. Accordingly, the focus servo control and the tracking servo control of the objective lens during recording are performed so as to enable the spot position of the second laser beam to follow the guide grooves on the selective reflection film 103 based on the reflected light of the second laser beam as the position control beam.
It is necessary for the first laser beam which is the mark recording beam to reach the bulk layer 102 formed on the lower layer side of the selective reflection film 103. Accordingly, in an optical system of this case, a first laser focus mechanism for independently adjusting a focusing position of the first laser beam separately from the focus mechanism of the objective lens is provided.
As the first laser focus mechanism, an expander for changing collimation of the first laser beam incident to the objective lens or the like may be realized.
During recording, when mark recording is performed with respect to a necessary information recording layer L among the information recording layers L set in advance, the first laser focus mechanism is controlled so as to change the focusing position of the first laser beam by an offset “of” corresponding to the selected information recording layer L. In the drawing, the case where the third information recording layer L3 is selected as the information recording layer L to be recorded and, in correspondence therewith, the focusing position of the first laser beam is changed from the selective reflection film 103 by the third offset of-L3 is shown.
As described above, the focus servo control of the objective lens is performed so as to follow the selective reflection film 103 based on the reflected light of the second laser beam. Accordingly, it is possible to realize a certain focus servo (follow-up to surface wobbling or the like) to the first laser beam.
In regard to the tracking servo of the first laser beam during recording, as described above, the tracking servo control of the objective lens is automatically performed so as to follow the guide grooves based on the reflected light of the second laser beam. In detail, the spot position of the first laser beam is controlled to the position which is a position beneath the guide grooves in the bulk layer 102.
Although not shown, since a mark string is formed in the bulk layer 102 during reproduction, it is not necessary to the position of the objective lens based on the reflected light of the second laser beam, like during recording. That is, during reproduction, the focus servo control and the tracking servo control of the objective lens is performed based on the reflected light of the first laser beam with respect to the mark string formed on the information recording layer L to be reproduced.
As described above, in the bulk recording method, the first laser beam as the mark recording/reproduction light and the second laser beam as the position control light are irradiated to the bulk type recording medium 100 through a common objective lens (by synthesis on the same optical axis). Thereafter, by performing control such that the position of the objective lens follows the guide grooves based on the reflected light of the second laser beam, the spot position of the tracking direction of the first laser beam follows the position beneath the guide grooves even when the guide grooves are not formed in the bulk layer 102.
However, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-71435, when a so-called tilt is generated, the spot position of the first laser beam is shifted from the spot position of the second laser beam.
That is, when the tilt is generated, since the bulk type recording medium 100 is not perpendicular to the common optical axis of the second laser beam and the first laser beam, the spot position of the first laser beam in the bulk layer 102 is not a position beneath the guide grooves, which the spot position of the second laser light follows, and thus a deviation therebetween is generated.
In Japanese Unexamined Patent Application Publication No. 2008-71435 discloses a technology of correcting the deviation between the spot positions of the first laser beam and the second laser beam by such a tilt.
In the related art, as disclosed as a second embodiment (FIGS. 17A and 17B) of Japanese Unexamined Patent Application Publication No. 2008-71435, tilt (slope angle) detection using a tilt sensor 165 is performed so as to correct the deviation between the spot positions.
As described in Japanese Unexamined Patent Application Publication No. 2008-71435, the tilt sensor 165 is configured to irradiate a sensor light beam so as to form a predetermined angle with respect to an optical disc 200 by a laser diode 167 provided for tilt detection and to detect the slope angle based on the result of detecting the spot position of the reflected light capable of being obtained from the optical disc by a photodetector 168.